Production of hydrofluoric acid and salts thereof.



R. S; SHERWIN. PRODUCTION 0F HYDIOFLUOHIC ACID A-ND SALTS THEHEDF.

APPLICATION FILED JULY 28. I9l5.

Patented Apr. 22, 1919.

2 SHEETS`SHEET I.

IIIII I IIIIN R. S. SHERWIN.

PRODUCTION 0F HYDROFLUORIC ACID AND SALTS THEREOF. APPLICATION FILED JULY 28. i915.

1901,325, Patented Apr. 22,1919.

2 SHEETS-SHEET 2.

WMM-T @Vi/I memes: U

RALPH s.' SHERWIN, oF EAST sT.

LOUIS, ILLINIS, vASSIG'II'OR T0 ALUMINUM COMPANY 0F AMERICA, 0'5' PITTSBURGH, PENNSYLVANIA, A CORPORATION .OF PENNSYL- VANIA.

PRODUCTION 0F HYDROFLUQRIC ACID AND SALTS THREOF.

Application led July 28, 1915. Serial No. 42,291.

To all 'whom it may concern:

Be it known that I, RALPH S. SHERWIN, a citizen of the United States, residing at East St. Louis. in tllecounty of St. Clair and State of Illinois, have invented certain new and useful Improvements in the Production of Hydroiiuoric Acid and Salts Thereo-f, of which the following is a full, clear, and eX- act description.

The invention which forms the subject of my present application relates to the production of hydrofiuoric acid and salts thereof, particularly sodium or other alkalinefluorids, and its chief object is to provide a ooniinuous and economical process for the purpose. Another object is to provide a process which can be performed without injury or inconvenience to the attendant workmen by exposure to acid fumes. To these and other ends the invention consists in the novel process and steps hereinafter described.

In practising my improved method or process I employ preferably a still of the type described in the copending application of Edwin S. F ickes, Ser. No. 828,436, and a condensing or absorbing` system of the kind described in my prior application Ser. No. 1,964. These devices are illustrated in the accompanying drawings, in which- Figure l shows tudinal sec-tion.

Fig. 2 is a plan view of the still, with the furnace setting or flue in horizontal section.

Fig. 3 is a crOSs section of the still on line 3 3 of Fig. l.

Fig. 4 is a cross section, on a slightly larger scale, of the retortv alone, showing the rotar)v agitator for stirring the nongaseous contents.

Fig. 5 is a detail view of the retort in elevation, showing means for cooling the shaft the Fickes still in longij of the agitator.

Fig. 6 is a view, partly in side elevation but partly in vertical longitudinal section, of the condensing or absorbing apparatus.

The still illustrated consists, in general, of a long,` tubular, stationary retort 10, inclosed in a suitable housing or setting 11, by which a gaseous heating medium is passed along the' retort, which medium may be the hot products of combustion from a furnace or lire chamber 12. Vertical baliies 13, extending alternately from opposite sides of the setting cause the smoke and gases to take a more or less tortuous course, thereby giv- Speciiication of Letters Patent.

ratentea am. as, raie.

ing a more ellicient utilization of the heat. At the end opposite the fire chamber the products of combustion llow downwardly and laterally through a ue 14 to the stack,

cured by any convenient means not shown. l

These lids or closures 16 may also be used to support hangers 16a for the shaft of the agitator, described hereinafter. The closure 17'a on the T 17 at the upper end of the retort, is provided with means for supplying the necessary acid producing materials, continuously or intermittently. In the drawing I have shown a simple hopper 18, with a gate valve 19, by which convenient quantities ofmaterial can be delivered into the retort at proper intervals. The closure 17a also has an outlet pipe 20 to carry olf the hydroiuoric acid vapor and conduct the same to a suitable condenser, for example that shown in Fig. 6. rllhe pipe, which is preferably made of lead or lined with lead, is provided with a valve 21 to regulate the rate of outflow.

At its lower end the retort terminates in a cross 22, having at the top a removable closure 23 and at the bottom a pipe 24 extending below the surface of the water in the pit 33, forming a water-seal. end closures 25, 26, is a shaft 27 extending through the retort at the axis thereof and provided with helically arranged radial arms 28 equipped at their ends with paddles or Scrapers 29 close to, but preferably not touching, the walls of the retort. At the lower end the shaft is connected with suitable driving mechanism, as for example an electric motor 30, by means of a worm 31 and worm gear 32.

Fluorspar and sulfuric acid, mixed in suitable proportions, are fed into the hot still or retort at the upper end through the hopper 18. In the retort it is thoroughly mixed by the revolving paddles 29, and gradually stiffens as it moves slowly down into the hotter parts. Finally it breaks up, part into powder and part into small balls or drogen iuorid, I-I'F) in the form of vapor,

and calcium sulfate (CaSO4) as a solid residue. The former goes ofi' through the lead pipe 20; while the residue, as fast as 'it reaches the cross 22, falls into the pit 33 and is removed from time totime in any convenient way. If necessary to -push the residue out, the lid 23 maybe removed for the purpose. U

The proportions of calcium iuorld and sulfuric acid may vary Widely in practice. Theoretically they should be in the proportion of 98 parts sulfuric acid to 78 parts calcium fluorld; but as natural calcium fluoridv (fluorspar) is always impure and sulfuric acid varies in strength, such proportions would involve more or less waste of the acid or fluorspar as any excess o f the latter would remain in the residue and any excess of the former as a part of the latter would simply volatilize or remain in the residue. denite proportions cannot be given, since dili'erent lots of iiuorspar and acid vary greatly, but the most economical proportions can easily be determined by analysis or trial or by both.

The temperature inside the retort or still at the hottest parts should not be less than about 315 C. (600ov F.), but may be in creased to any degree which will not injure .the retort or soften the agitator shaft so as to cause it to twist, bend` or spring. To prevent overheating of the shaft' and permit higher temperatures to be used, the shaft may be hollow, as in Fig. 5, -to carry water or other cooling medium supplied to the lower end by a pipe 34 and dicharged at the upperl end by a pipe 35. The couplings 36 are of any suitable kind, permitting the shaft to turn. This shaft should, in most cases, revolve quite slowly. In a retort three feet in diameter and about sixty feet long the shaft should require rather more than a minute to make one revolution, and the material should require not less than about three hours (better four) to pass from the inlet to the outlet end. If the rate of progress is too fast the mixture is heated too rapidly and causes volatilization of the sulfuric acid, thus causing a loss of fluorin and giving a considerable amount of sulfuric acid in the hydrofluoric acid condensed. If the retort is inclined, with the inlet for the liuorspa-r and sulfuric acid at the higher end, lthe paddles or scrapers 29 may be parallel to the 'axis of the retort, as the inclination'of the latter, together with the agitation produced by the paddles, will cause the material to move through the retort ata fast enough rate.

I n connection with the still above described, two condensing or absorbing chainbers A, B, Fig. 6, are employed, onedesignated the primary and the otherthe` secondary condenser-orabsorber. Each is in the form of a box made of suitable material, for example the first of lead and the other of wood, or both lead or both wood, elongated vertically and provided with bailes C, D, those in the primary absorber, and if desired those in the other also, being spaced successively farther apart from the top downward. jl The acid vapors and any other gas or gases mixed therewith 'enter the primary absorber A at the bottom through a conduit E which is connected with or is a continuation of the gas-outlet pipe 20 of the still shown in Fig. 1. At the top of the absorber A is a water-inlet F, provided with a regul-ating valve F. Entering from the conduit E the gases rise and encounter the water flowing over the baffles, 'which are preferably spaced -closer together at the top to compensate for the rapid absorption of the gases and vapors by the water. At the bottom of the absorber A is an outlet G for the acid, discharging through a water seal.

H. The lunabsorbed or undissolved vapors and "other gases leave the primary absorber A at the top and are conveyed by a conduit I to the lower part of the secondary absorber B, which has at the top a liquid inlet J provided with a valve J Water maybe delivered by the latter if desired, but I prefer to employ an alkaline solution, as will be described hereinafter.. i

Inl the manufacture of aluminum iuorid, or cryolite, and other iiuorids, it is desirable to have the acid of s'uicient strength, or of suflici'ently high temperature, to cause it to re` act readily with the alumina or other base of the material used. Since the absorption of hydrofluoric-acid vapors in water liberates a considerable amount of heat, I am able to obtain the hydrofluoric acid solution at any desired `temperature 'by properly regulating the supply or temperature, or both, of water to the absorber. By this means, both the sensible heat of the gases and vapors entering the absorber and the 'heat liberated by the condensation or absorption are utilized for the purpose of bringing the acid solution to any desired temperature. Here the height of the absorber, and the number and spacing of the bales (successively farther apart from the top downwardly), play an important part, in that by suitable proportioning of these features the absorption with a small quantity of water is increased, thereby giving not only a stronger solution but also giving the solution a higher temperature, thus increasing the efliciency o f the solution vin the subsequent production of iuorids. By increasing the number of bailes and decreasing the amout of liquid entering at the top the strength Aof the acid solution in the lower part of 'the absorber can be able cooling tower or other carried to a high degree of concentration. This is due in part to the increased absorption of the acid vapors, and in part to the evaporation of the water in the absorber. If the temperature rise is suicient to cause the acid solution descending in the lower part of the absorber to boil (under the reduced pressure in the absorber) the evaporation will be more rapid, and the concentra.- tion, Within certain'limits, will be greater. A boiling solution o f hydrofluoric acid in water may give oft' both hydrofluoric acid and Water vapor, but `the vapor is greatly in excess until the acid solution reaches a concentration of about 30 per cent. The evaporation by boiling of the descending stream in the lower part of the condenser has the advantage of removing the excess heat from the liquid, so that it is capable of absorbing more acid from the strong acid vaporsl entering at the bottom. The water vapor formed in the lower part of the absorber may be condensed in the upper part lby 'the incoming liquid, or part of it may pass into the secondary absorber. If for any reason it is found desirable to keep the solution from boiling, the water can be delivered at a lower temperature. This may at times involve cooling the water, for which purpose the Water may pass through a suitcooling apparatus F before reaching the absorber. The acid solution which collects at the bo-ttom of the absorber may also be cooled, if desired, in any convenient Way; as for example by its flow through the coil G in the vessel G through which cold water is circulated. The Water-seal H of course allows the acidsolution to pass freely out but prevents the entrance of air.

The non-condensable gases, and any other gases and vapors that are not condensed or absorbed in the primary absorber, pass to the secondary absorber and there encounter a descending stream of a solution of sodium carbonate or other suitable alkaline solution. Here, the acid vapors present react with the base of the solution, and the liquid passes out through a liquid-seal into the tank K, whence it is delivered to the supply pipe .I by means of apump indicated diagrammati-4 cally at L; old solution being withdrawn from and fresh solution added to that in the tank continuously or intermittently at a suitable rate. The precipitated fluorid also collects in the tank and is removed continuously or intermittently as may be desired, by

any convenient means not shown. If a soda solution is used the precipitate is sodium iiuorid, which may be used in the manufac-` ture of cryolite or other double fluorid of sodium or aluminum. The gaseous residue passes out of the absorber B at the top thereof, through a suitable exhauster M, and 1s discharged from a stack not shown; the eX- hauster serving to create the vacuum, in the absorbers and in the acid-vapor enerator or still, whichproduces the flow o vapors and gases from the generator through the absorbers. A considerable part of the vapors admitted to the secondary absorber is condensed therein by passing upwardly throughy the descending stream of alkaline liquid. It may at times happen, however, that the vapors carry so much heat into the secondary absorber-1(particularlyif the solution in the primary absorber is boiling) that the solution in the secondary becomes too hot, with the result that condensation of the vapor is diminished and too much vapor passes out through the exhauster. In such case the so- 'lution can be cooled in any convenient manner, as by means of a cooling tower K, through which the liquid flows on its way to the top of the absorber. As the solution is circulated through the absorber more and more of its carbonate is removed by reaction with the hydrofluoric acid. Accordingly the absorber is replenished from time to time by dissolving fresh carbonate in the liquid in he tank K, or fresh solution is added, or

oth.

From the foregoing it will be seen that the process is continuous, the acid vapors being continuously drawn from the still and through the absorbers, and the waste or solid residue from the still is continuously discharged through the water seal 33. The economy thus secured has in practice been found to be very great. Another important advantage Hows from the fact that the operations take place in a partial vacuum, so that there can be no escape of corrosive fumes into the air adjacent to the apparatus.

It is thus possible for the workman to open the still, as often as desired, for the purpose of supplying raw material thereto, without suffering injury or even inconvenience or discomfort. This contributes to the wellbeing of the workmen and hence makes them more eflicient, thereby contributing, though indirectly, to the economy of the process. The process also possesses another important advantage, which can be described as follows. In the manufacture of aluminum fluorid, or cryolite, it has been'found exceedingly difficult to precipitate the fluoride completely from the solution resulting when hydroluoric acid is neutralized with aluminum hydrate, sodium hydrate, or other materials containing alumina or soda. If dilute solutions of fluoride, resulting from the manufacture of aluminum fluorid or cryolite, are returned to condensers of the prior types, in which the hydroiiuoric acid-vapors are passed through the water solution in the tank, a precipitate is formed which clogs the vapor pipesand renders the operation'of the still dangerous. In the present invention the vapors do not pass through a body of liquid in a tank but through a stream of water or solution, and any precipitate formed is washed down, and oi the bailles, by the continuous stream and passes out through the water seal at the bottom.

It is'to be understood that the invention is not limited to the particular apparatus herein described, but can be practlsed by other means without departing from 1ts spirit.

I claim:

1. The herein described continuous process of producing luorids and hydrouoric acid, which consists in continuously generating hydrofiuoric acid gas in a closed chamber or retort, applying suction to the retort and drawing the acid gas through a stream of absorbing liquid owing through a closed absorbing chamber, drawing unabsorbed gas from the latter chamber and through a stream of liquid flowing through a second closed absorbing chamber and containing in solution a compound capable of reacting with the hydrofluoric acid and producing a iluorid, and collecting the acid solution from the first absorbing chamber and the iiuorid from the second, the generation, and absorption reaction all taking place under pressure less than atmospheric.

2. The herein described continuous process of producing hydroiiuoric acid and salts thereof, which consists in continuously generating hydroiuoric acid gas in a closed retort, applying suction to the retort and drawing the acid gas therefrom upwardly through a closed absorber and through a stream of absorbing liquid descending therein, drawing unabsorbed gas by suction from the top of the absorber and upwardly through a second closed absorber through which is descending a stream of liquid' containing in solution a compound to react with the acid gas and produce the desired luorid,

while withdrawing liquid from the bottom' of the second-named absorber and delivering it into the top thereof, collecting acidladen liquid from the bottom of the iirst absorber and iiuorid from the bottom of the second, and from time to time replenishing the second absorber, the generation, absorptions and reactions taking place under pressure less than atmospheric.

3. The herein described continuous process of producing hydroiiuoric acid and salt thereof, which comprises continuously generating gases containing hydroluoric acid under pressure less than atmospheric, drawing the acid gases against a counter current of downwardly {iowing sub-divided, agitated, absorbing liquid,while said gases are still under pressure less than atmospheric, whereby the ases are caused to pass through the fal ing liquid, drawing the unabsorbed gases by suction upwardly against a counter current of an agitated, sub-divided, absorbing liquid containing a comthe closed chamber to draw the acid gas' therefrom, drawing the acid gas by suctlon upwardly through a closed absorbing chamber and simultaneously delivering an absorbing li uid to the top of the absorbing chamber w ereby the gas is caused to pass through a descending stream of the liquid, and collecting the liquid at the bottom of the absorbingchamber, the generation and absorption of the acid gas taking place under a pressure less than atmospheric. l

5. The herein described method which comprises the successive steps of (a) generating hydrofluoric acid, (b) absorbmg a portion of the hydroiuoric acid in water, (c) absorbing at least a portion of the remaining hydroiuoric acid rin a liquid containing a base, all three of these operations being formed under pressure lower than atmospheric.

6. The herein described process for the purpose described, which consists in continuously generating hydroiiuoric acid gas in a closed retort under pressure less than atmospheric whereby the retort may be opened from time to time for the introduction of acid-producing materials without the escape of gas, drawing the acid gas by suction from the retort and through a closed absorbing chamber, passing a stream of absorbing liquid through the chamber in the opposite direction to the iow of gas, at a rate and initial temperature adapted to cause boiling of the liquid by the heat of absorption, and collecting the acid-laden liquid at the bottom of the chamber.

7 The herein described process, comprising drawing hydroiluoric acid gas by suction through a closed absorber, passing through the absorber a solution containing a reagent to react with the acid gas for the production of a iluori-d, returning the solution to the absorber repeatedly, and removing iiuorid therefrom. l

8. The herein described process which comprises treating gases containing hydroluoric acid, in the formof an upwardly flowing stream of said gases, with an absorbent liquor containing a .reagent capable of reacting with the said acid to produce a fluorid, while agitating and sub-dividing the said liquor.

9. The herein described process which comprises drawing gases iuoric acid upwardly in contact with a downwardly flowing, agitated and sub-divided absorbent liquid containing analkal in solution, while malntaining said gases, atmospheric, and

under pressure less than circulating the absorbent liquid.

10. In the production acid solution, the improvement which'com- 10 prises bringing a current of hydroiluoric containing hydroof hydrofluoric acid gas into contact with a counter owing current of Water, under pressure below atmospheric, while so regulating the amount and temperature of the water relative to the amount and temperature of the hydrofluoric acid gas, `as to produce a substan- 'tially boiling hydrofluoric acid solution.

In testimony whereof I hereunto aix my RALPH S. SmRWIN.

' signature. 

